1. Field of the Invention
The present invention generally relates to a cryogenic refrigerator and more particularly, to means for supporting piston/displacer for use in such a cryogenic refrigerator.
2. Description of the Related Art
A conventional stirling refrigerator is designed, for example, to cool infrared sensors to as low as 77K and generally comprises a compressor, and a cold finger connected to the compressor through a conduit. The compressor includes a vertical cylinder fit within the upper end of a compressor housing, and a piston mounted for reciprocal motion within the cylinder. A plurality of flat piston suspension springs are horizontally disposed within the compressor housing to support the piston so as to prevent rubbing contact of the piston with the inner wall of the cylinder and thus, wear of the piston and the cylinder. Each of the piston suspension springs is in the form of a circular disk and includes a plurality of spiral slits to provide a plurality of spiral arms (see FIG. 16). The spiral arms are vertically deflected as the piston is reciprocated within the cylinder.
A plurality of annular outer retainers are secured to the inner wall of the housing and arranged to sandwich the outer peripheral edges of the piston suspension springs. Similarly, a plurality of annular inner retainers are secured to a piston rod and arranged to sandwich the inner peripheral edges of the piston suspension springs. In this arrangement, however, the spiral arms are susceptible to fatigue failure as a result of periodic application of local stresses during the normal operation of the compressor. This is due to the fact that the inner and outer ends of the spiral arms are held substantially in point contact with the circumferential edges of the inner and outer retainers (see FIG. 17) and subject to high stress concentration as the spiral arms are deflected.
The cold finger includes a low temperature cylinder within which a displacer is reciprocally moved. The displacer has a body and a rod extending downwardly from the body. The interior of the low temperature cylinder is divided by the displacer into two chambers, namely, a low temperature chamber above the displacer, and a high temperature chamber below the displacer body. A regenerator is mounted within the displacer body. A gas port is formed in the displacer body to provide a fluid communication between the low temperature chamber and the high temperature chamber via the regenerator. A first sleeve is fixed within the lower part of the low temperature cylinder to surround part of the displacer body. A second sleeve is fixed below the high temperature chamber. The displacer rod extends through the second sleeve and into a spring chamber. A plurality of flat displacer suspension springs (see FIG. 18) are mounted within the spring chamber to support tile displacer so as to prevent rubbing contact of the displacer with the first sleeve and the second sleeve and thus, wear of the displacer and the sleeves as the displacer is reciprocated. Each of the displacer suspension springs is in the form of a circular disk and has a plurality of spiral slits to provide a plurality of spiral arms. The spiral arms 30a are vertically deflected as the displacer is reciprocated.
A plurality of annular outer retainers are secured to the inner wall of the spring chamber to sandwich the outer peripheral edges of the displacer suspension springs. Similarly, a plurality of annular inner retainers are secured to the displacer rod to sandwich the inner peripheral edges of the displacer suspension springs. In this arrangement, however, the spiral arms are susceptible to fatigue failure as a result of periodic application of local stresses during the normal operation of the displacer. This is due to the fact that the inner and outer ends of tile spiral arms are held substantially in point contact with the circumferential edges of the inner and outer retainers (see FIG. 19) and subject to high stress concentration as the spiral arms are deflected.